It is conventional to mount many windows in homes so that they can be opened for ventilation. Windows mounted on vertically oriented hinges are generally referred to as "casement" windows. Windows mounted on horizontal hinges are referred to as "awning" type windows. It is conventional to provide a hand cranked winder to move the window through its range of motion from the opened to the closed position. As the window approaches the closed position a latch is usually provided to seat the window and to lock it in the closed position. Typically, a keeper attached to the window sash mates with a latch assembly which is attached to the window frame or sill. The latch captures the keeper and operation of the latch draws the window into the closed position where it is locked. In the closed position the window is seated in the frame and compresses weather stripping to seal the window assembly.
In many applications the window may sag and alignment between the keeper and the latch may vary over time. In these applications it is difficult for the latch to capture the keeper and effectively close the window.